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Actual acid mine drainage (AMD) containing a high concentration of sulfate (∼1,000 mg·L−1), dissolved metals, uranium, rare earth elements and yttrium (REY) was treated using a down-flow fixed-structured bed biological reactor (DFSBR). The reactor was operated in a continuous flow mode for 175 days and the temperature was maintained at 30 °C. The synthetic AMD was gradually replaced by the actual AMD in 20, 50 and 75% of the total medium volume. Sugarcane vinasse was used as the electron donor and the influent pH of the reactor was decreased from 6.9 to 4.6 until the system collapsed. REY elements and transition metals were removed from the actual AMD and precipitated in the down-flow fixed-structured bed reactor. Sulfate reduction achieved 67 ± 22% in Phase II and chemical oxygen demand (COD) removal was above 56% in Phases I and II. Removal of La, Ce, Pr, Nd, Sm and Y was higher than 70% in both Phases II and III while Fe, Al, Si and Mn were removed with efficiencies of 79, 67, 48 and 25%, respectively. The results highlighted the potential use of DFSBR in the treatment of AMD, providing possibilities for simultaneous sulfate reduction and metal and REY recovery in a single unit.

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Two anaerobic fixed-structured bed reactors were fed with synthetic wastewater simulating the soluble fraction of sugarcane vinasse to evaluate the interference of sulfidogenesis on methanogenesis. The reactors running in parallel were subjected to the same operating conditions. The influent organic matter concentration (in term of chemical oxygen demand (COD)) remained close to 4,000 mgCOD L(-1) and the hydraulic retention time was 24 hours. One reactor, the methanogenic (control reactor), received sulfate only to provide the sulfur required as a nutrient to the methanogenic biomass. The other one, the sulfidogenic/methanogenic reactor (SMR), received sulfate concentration corresponding to COD/sulfate ratios of 4, 5 and 3. In the last phase, the COD removal efficiencies were higher than 96% in both reactors and the SMR achieved 97% of sulfate removal efficiency (COD/sulfate ratio of 3 and influent sulfate concentration close to 1,300 mgSO4(2-) L(-1)). Both reactors also had similar methane yields in this phase, close to 350 mLCH4 gCODremoved(-1) at standard temperature and pressure. These results indicated no significant inhibition of methanogenic activity under the sulfidogenic conditions assessed.

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BACKGROUND Textile wastewater is known for its polluting potential and toxicity. Biological, affordable treatments are especially desirable in developing countries to fulfill legal and ecological demands during its treatment. RESULTS The performance of an anaerobic structured‐bed reactor (AnSTBR) treating synthetic textile wastewater containing Direct Black 22 azo dye (DB22; 0.06 mmol L–1) and sulfate ions (200 mg L−1) was evaluated. The reactor hydraulic retention time (HRT) was 24 h and ethanol was used as the electron donor (1000 mgCOD L−1). The AnSTBR achieved an average decolorization efficiency of 68 ± 5%, chemical oxygen demand (COD) efficiency of 77.7 ± 9.2% and sulfate removal of 77.3 ± 5.2%. Toxicity tests showed lower toxicity of the treated effluent to Ceriodaphnia dubia. Despite that, the AnSTBR effluent was still highly toxic to mammalian cells. The metabarcoding technique of the 16S rRNA gene sequencing revealed a consistent community of sulfate‐reducing and azo‐degrading bacteria. CONCLUSION Metagenomic data revealed a promising development of the inoculum in the AnSTB structure. The AnSTB reactor configuration may be a promising alternative for DB22 dye removal from textile wastewater containing sulfate. © 2021 Society of Chemical Industry